The present invention relates to inflated bladder-type sports balls, including those used for leisure activity, and particularly, to ones having a covering of foamed plastic material with an integral, external non-foamed skin.
Inflated bladder-type sports balls made presently belong to two main categories: ones which have an external cover or layer constituted of hand-sewn elements, for example, of leather or a synthetic material, such as polyurethane, and those having a cover which is not obtained by manual sewing, but by molding in place an external layer, by manual or mechanical means (e.g., with a spray gun for a composition comprising polyurethane). The balls of the second category are, in contrast with those of the first category, often called non-hand-sewn balls.
In other respects, the conventional technique for manufacturing balls is based on the use of an inflated internal bladder or bag, generally made of rubber, which, in most cases, is covered by a textile component made out of fibres or filaments made of a natural or a synthetic material, these fibers or filaments being, for example, progressively wound on the bladder. In order to ensure the integrity of the textile layer, it is combined with a composition, which is generally vulcanizable or curable, especially with a natural or synthetic rubber. The final external coating is then applied on this composition.
Another type of ball is also known in the art, which does not include any bladder, but has an equivalent internal carcass obtained directly from a polymeric synthetic composition, which can be formed in a conventional manner, e.g., by molding and, more particularly, by rotary molding (e.g., rotary slush casting) technique in which centrifugal forces produce rotational dispersion of the polymeric composition and the formation of a hollow shell, with a more or less regular wall which is more or less dimensionally stable.
The methods, which have been mentioned hereinabove, are well known to the persons skilled in the art and it is, therefore, not necessary to describe them in more detail.
A person skilled in the art would tend to try to improve the characteristics of conventional balls and to simplify their manufacture. It is especially important to obtain balls which have a "behaviour", or response, giving full satisfaction to the user, having a long, useful life and which can be manufactured more economically than the conventional balls.
Foam or sponges with integral skin are already known in the automotive industry, the furniture industry and the shoe industry. Also, foams or sponges with a semirigid or flexible integral skin are known, but their characteristics are not adapted for the manufacture of balls because they have a reduced resilient memory and too high a glass-transition temperature (generally over -40.degree. C.).
It has been suggested in the prior art to use polyurethane foams for manufacturing balls.
For example, French Patent 2,572,674 discloses the overmolding of an internal bladder or carcass, obtained by rotary molding, by injecting around the bladder or carcass, a polyurethane composition which is provided in the form of a polymerizable liquid. This French patent teaches a ball-manufacturing process providing balls with an external layer that has the form of a cellular material, but it does not disclose at all a ball cover that includes a foam with an integral skin. On the contrary, when considering the disclosed manufacturing conditions, it appears that the polymerizable liquid is injected under low pressure and the mold is heated. These practical indications would not allow one to obtain a foam with an integral skin, and especially such a foam having the physical characteristics and parameters which are indispensable for manufacturing balls when using a foam with integral skin.
U.S. Pat. No. 1,614,853 teaches the manufacture of tennis balls, in which the internal carcass of the ball is surrounded by a thin cover in cellular rubber which may include a skin resulting from a molding step. For the final formation of the ball, the pieces cut out from the cover may be cemented or glued on the internal carcass. This patent does not disclose use of polyurethane or polyurethane-polyurea foam or sponge with an integral skin, and, especially does not give any indication about the physical characteristics and parameters to be complied with for manufacturing larger balls, such as footballs, rather than tennis balls.
U.S. Pat. No. 4,462,590 relates to the manufacture of balls, especially of footballs (for playing American football), having an external part or cover and a padding layer which is said to improve the "grip" provided to the user of the ball, and which layer may be constituted of cellular polyurethane. The disclosure of this last-mentioned patent, also relates to the construction of the internal bladder of the ball. This patent discloses, therefore, a ball, especially a football, with an external layer made out of two distinct elements, i.e., the external cover proper and the padding layer.
Belgian Patent 411,755 describes the manufacture of balls made of leather, starting from separate panels which are sewn. This patent has for an object provision of a ball having a structure with a small tongue allowing a user to reach more easily the internal portion of the ball.
French Patent 1,488,920 describes a conventional method for manufacturing balls of a type having a bladder, more particularly basketballs. The pieces of the external cover, which are made of vulcanized rubber, may be obtained starting from plates.
U.S. Pat. No. 3,112,52I discloses a very sophisticated apparatus for manufacturing golf balls. It is particularly concerned with means for exactly locating the core of the golf ball inside a mold cavity, so as to allow the filling of the cavity with a composition of liquid polyurethane, thereby forming a polyurethane layer of uniform thickness at the outer periphery of the core of the ball.
French Patent 2,215,249 discloses the manufacture of panelled balls, by cutting the panels which provide the exterior of the ball from preconstructed sheet material having a compounded structure.